Polymethacrylate pour point depressants (PMA PPD's) are well known in the lubricating industry. Many attempts have been made to produce PMA PPD's that improve the low temperature viscometrics of various lubricating compositions.
PPD additives improve the low-temperature performance of an oil by modifying the wax crystallization process. A wide variety of chemical types are currently available, and include polyalkylmethacrylates, styrenated polyesters, alkylated polystyrenes and alkylated naphthalenes. The present invention is directed to novel alkyl (meth)acrylate polymers which exhibit desired low temperature viscometrics. More specifically, the invention is directed to PMA PPDs that exhibit outstanding low temperature properties in lubricating oils for applications such as crankcase lubricants and automatic transmission fluids. The oil chemist is constantly searching for PPDs that achieve optimum low-temperature performance at low concentrations. The present invention addresses the need for an improved PPD.
U.S. Pat. No. 2,655,479 to Munday et al. claims a pour point depressant composition consisting of a blend of two copolymers, the first copolymer having an average side chain length of about 12.7 while the second copolymer has an average side chain length of about 11.2.
U.K. Patent No. 1,559,952 discloses a mixture of two classes of oil soluble polyalkyl (meth)acrylates as pour point depressants.
U.S. Pat. No. 4,146,492 discloses lubricating oil compositions comprising between about 0.5 and 30 wt. % of a specifically defined ethylene-propylene copolymer and between about 0.005 to 10 wt. % of a neat interpolymeric polyalkylacrylate of (A) C.sub.1 -C.sub.15 alkylacrylate and (B) C.sub.16 -C.sub.22 alkylacrylate having a weight ratio of A:B of between about 90:10 and 50:50, a molecular weight of from 1000 to 25,000 and an average alkyl side chain length of between about 11 and 16 carbons.
U.S. Pat. No. 4,867,894 discloses pour point improving additives for mineral oils comprising from 10 to 30 mole percent methyl methacrylate, 10 to 70 mole percent of a linear C16 to C30 alkyl methacrylate, from 10 to 80 mole percent of a C4-C15 linear alkyl methacrylate and/or a C4 to C40 branched methacrylate, and from 0 to 30 mole percent of a free-radically polymerizable nitrogen-containing monomer having dispersing action.
U.S. Pat. Nos. 5,312,884 and 5,368,761 disclose copolymers useful as pour point depressants for lubricating oils comprising 15-67 mole percent C8-C15 alkyl (meth) acrylates, 3-40 mole percent C16-C24 (meth) acrylates, and from greater than 30-65 mole percent C1-C4 methacrylates. These patents do not teach copolymers containing the specific monomers in the specific proportions required by the present claims.
U.S. Pat. No. 5,534,175 discloses copolymers of unsaturated fatty esters derived from 12-20 mass % of a C1-C3 (meth) acrylate, 45-72 mass % of a C11-C15 (meth) acrylate and 14-30 mass % of a C16-C25 (meth) acrylate.
EP 0 236 844 B1 teaches pour point improving agents derived from methyl methacrylate.